The present invention relates to a safety valve of the type comprising a flap sealingly applied under normal conditions, against a seat under the action of resilient means, e.g. a calibrated spring, so as to obturate an opening made in a fluid-containing enclosure, said flap being biased away from said seat against the action of said spring, whenever the fluid-pressure rises beyond a given level.
As is well known, the operation of such a valve is controlled by the pressure within said fluid-containing enclosure. Whenever the pressure within said enclosure can be considered as normal, the flap is maintained sealingly applied against said seat by the calibrated spring. On the other hand, whenever the fluid-pressure reaches the value determined by the spring calibration, the flap is raised from its seat and lets the fluid flow until the pressure within the enclosure be again lower than said limit value. When such is the case, the flap is again sealingly applied against the seat and closes the valve. If the pressure within the enclosure continues to rise, the valve is again caused to open, whereupon it is again caused to close. Such movements of the valve may happen to occur repeatedly, in which case they submit the flap to the so-called "beat phenomenon".
When the fluid contained in the enclosure is a compressible one, it acts in the manner of a mattress and it damps down said beats, so that the frequency of the latter remains relatively low, without any damaging consequences as regards the whole equipment. On the other hand, when the fluid contained in said enclosure is incompressible, the beats are not damped down, so that the frequency thereof becomes very high. There occurs then an overheating in the guiding regions of the moveable parts and, in particular, in the flap. In some cases, such an overheating can be important enough for generating microwelds and inducing the scuffing of said movable parts, with the possible consequence of unfavorably maintaining the valve open and exhausting the enclosure. Moreover, in some cases, in particular when said valve belongs to the water-circuit of a nuclear power-plant, the fortuitous drainage of said circuit may lead to severe consequences as regard the whole installation.
The object of the present invention is to provide a safety valve of the above described type, capable of being installed in an enclosure filled with an incompressible fluid, while being free from the drawbacks of the safety-valves of the prior art. It must be noted however, that the scope of the present invention is not restricted to safety-valves adapted to be mounted in enclosures filled with an incompressible fluid, and that the invention also covers valves to be mounted in enclosures filled with a compressible fluid.